The present invention is directed to the managing of cervical spine injuries in general, more particularly to a new intervertebral stabilization implant for the managing of a cervical spine injury. The vertebral column consists of 33 vertebrae superimposed upon one another in a series which provides a flexible supporting column for the trunk and head. The vertebrae are separated by fibrocartilaginous intervertebral disks and are united by articular capsules and by ligaments. Of the fundamental 33 vertebrae, five are fused into the sacrum, and four combine in forming of the coccyx in the adult. The remaining 24 vertebrae are classified as seven cervical, twelve thoracic, and five lumbar.
The cervical vertebrae are the smallest of the series and are readily distinguishable by the presence of a large oval foramen in each transverse process. The body is small and somewhat broader from side to side than from front to back. The superior surface of the body is concave transversely with projecting lips on either side. The inferior surface is concave anteroposteriorly; its anterior lip projects downward to overlap the superior surface of the vertebrae below. The inferior surface is convex transversely to fit the transverse cavity of the superior surface of the next adjacent vertebrae. The pedicles project lateralward as well as backwards and spring from the body midway between its superior and inferior surfaces, so that the superior vertebral notch is steep as the inferior. Laminae are thinner above than below and enclose a larger, triangular vertebral foramen for the accommodation of the upper and larger portion of the spinal cord. The spinous process is short and bifid. The articular processes from prominent lateral projection from the junction of pedicles and laminae and three flat, oval facets. The superior facet are directed upwards, backwards and lightly medialward; the inferior facets face oppositely. Each transverse process is said to be perforated by the transverse foramen for the passage of the vertebral artery and vein and the vertebral nerve plexus. Actually, the "costo-transverse" foramen is located between the transverse process posteriorally and a costal process anteriorally.
Various devices have been developed for the management of cervical spine injuries. One such device is a halo which consists of a stainless steel tiara affixed in four opposite positions to the skull by pins that penetrate the skin in external table. Treatment process includes maintaining the patent in traction for six weeks, then utilizing a "Minerva Jacket" for an additional six weeks or more. Most patients are stabilized with the device after twelve weeks. During the three month interval while intrinsic stability to the fractured spine is regained, the halo, either suspended on a plastic jacket or attached to a pelvic hoop permits early, safe mobilization under strong skeletal fixation. One of the disadvantages with halo braces is that they are likely to leave patients susceptible to neck pain developing late after cervical spine injury. It has been reported that about a third of the patients in halo braces sooner or later encounters instability or develops neck pain. (Convention Reporter, report on the Sixth Annual Scientific Meeting of the American Spinal Injury Association, Volume 10, No. 17, August, 1980).
Another device for stabilizing cervical injuries is an acrylic prothesis of the fifth cervical vertebra in multiple myeloma, as was reported in The Journal of Neurosurgery, Volume 35, p. 112, July 1971. In the procedure described in the above article, the collapsed fifth vertebral body is removed with rongeurs and curettes, exposing the anterior surface of the dura, the nerve roots, and portions of the vertebral arteries. The annulus and disks are removed from the interior surface of the fourth cervical vertebra and from the superior surface of the sixth cervical vertebra. A thick layer of Gel Foam moistened with saline was placed anterior to the dura. A piece of thin Tantalum shaped into a half cylinder was placed over the Gel Foam. A tantalum screw was then inserted into the interior surface of the body of the fourth cervical vertebra and into the superior surface of the body of the sixth cervical vertebra protruding into the fifth cervical interspace for a distance of 1 cm. With the use of a cervical traction apparatus the normal fifth cervical vertebra interspace was established. Methyl methacrylate powder and isomer were then mixed and shaped around the protruding screws in the form of a normal cervical vertebra. The disadvantage with the above described method is that it usually involved three cervical vertebrae and requires the removal of the fractured vertebra.
A metal prosthesis for the cervical vertebrae was disclosed in the Journal of Neurosurgery, Volume 42, May 1975, p. 562. The prosthesis described is a quadrilateral cylindrical member with a window in the front. The sizes of the prosthesis correspond to that of a cervical vertebra. The technique requires the removal of the affected vertebra and insertion of the prosthesis through an anterior approach, as in Cloward's anterior body fusion. Collapsed vertebral body is removed with rongeurs and curettes exposing the anterior surface of the dura. Annulus and disks were also removed from the upper and lower surfaces of the affected vertebra. Again, the procedure described in that reference requires the removal of the fractured vertebra and the involvement of two additional vertebrae. For other lesions of a destructive nature, like malignancies, the stabilization of the cervical spine has required the use of a combination of methacrylate and metal screws in normal bone above and below the destructive area in the vertebral body. Alternately, a cylinder-like device made of Tantalum is used to serve as a mold for the methacrylate that is used to replace the absent vertebral bodies. This latter approach has had limited success.
Other method of treating the fractures of the cervical spine include posterior stabilization surgical procedures which require the involvement of four vertebrae as a general rule and require the permanent immobilization of three of the intervertebral spaces. Long range effects in the rest of the cervical spine tend to increase with time. Usually, a second incision is required in order to obtain a bone graft. Another procedure is an anterior cervical fusion. This procedure requires a bone graft, usually from the ilium. The stability of the fracture site with good reduction after surgery would require at least five to six weeks. In the meantime, traction, collar, bed rest or other techniques must come into play in order to prevent destabilization of the reduced spine.